Field of the Invention
This invention relates generally to a system and method for estimating vehicle speed and, more particularly, to a system and method for a secondary or redundant estimation of vehicle speed in the event that a primary speed estimation module fails, where a secondary speed estimation module employs sensor inputs from a 6 degree-of-freedom (DOF) inertial measurement unit (IMU), a GPS receiver and range sensors.
Discussion of the Related Art
Vehicles are becoming more autonomous or cognitive with the goal being a completely autonomously driven vehicle, i.e., vehicles that are able to provide driving control with minimal or no driver intervention. Adaptive cruise control systems have been available for a number of years where not only does the system maintain a set speed, but also will automatically slow the vehicle down in the event that a slower moving vehicle is detected in front of the subject vehicle. Vehicle control systems currently exist that include autonomous parking where the vehicle will automatically provide the steering control for parking the vehicle. Also, control systems exist that may intervene if the driver makes harsh steering changes that may affect vehicle stability and lane centering capabilities, where the vehicle system attempts to maintain the vehicle near the center of the travel lane. Future vehicles will likely employ autonomous systems for lane changing, passing, turns away from traffic, turns into traffic, merging into traffic, passing through or turning at intersections, etc.
Various active safety control systems, driver assist systems and autonomous driving operations on vehicles, such as electronic stability control (ECS), adaptive cruise control (ACC), lane keeping (LK), lane changing (LC), etc., require highly robust and precise modules for estimating various vehicle dynamics. Such modules are necessary to provide knowledge of the vehicle position and velocity to control the vehicle.
Active safety control for the systems discussed above, and others, rely on accurate vehicle speed estimation for proper performance. Currently, these types of proposed systems rely on wheel speed sensors and other vehicle kinematic inputs to provide the vehicle speed estimation. However, sometimes sensors and control modules that determine vehicle speed fail or operate incorrectly, where loss of vehicle speed could be serious. Certain automotive safety requirements, such as ASIL-D, require redundant vehicle speed estimation processes in the event of failure of the primary estimation processor. For example, for those systems that require active control, the control systems are required to provide accurate speed estimation for five seconds after the failure event so as to give the driver time to take control of the vehicle. It would be desirable to provide such redundant speed estimation processes using existing hardware on the vehicle to reduce vehicle cost.